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Preventing/Limiting inrush current on L7986

Question asked by Henro Ritchie on Jan 12, 2017

Hi All


I am currently testing a power supply system with a bulk power supply backplane (30V, 12A) and cards that slot in on the backplane. The cards come in various different flavors (24V, 12V, 5V) all using L7986A as the SMPS. The 24V has its own layout (board) while the 12V and 5V use the same board, just configured for the different voltages. 


All the boards seem to be very susceptible to inrush current when turning the system on. In most cases, the L7986 literally burns with smoke, and sometimes flames. I am sure it is not a voltage spike. A small value resistor (high wattage) or NTC seems to alleviate the problem, although I am still not happy with the solution. I have used the L7986 on numerous other designs never experiencing this problem.


Any help or ideas are welcome. I can post more information and schematics if required.


Best Regards

Henro Ritchie